Method for molding microstructures and nanostructures

ABSTRACT

A method for moulding microstructures and nanostructures on a layer that can be thermally structured by means of a structured mould using an electromagnetic radiation producing the required heat. A mechanically stable mould and a stable base are used. By absorbing a beam with high energy density, either the mould or the base is heated on the surface due to the low penetration depth of the beam. The generated heat is transmitted to the layer, and the softened layer is then structured by means of the mould. The layer that is used is as transmitting as possible and is penetrated by the beam before being heated. The heat required for moulding can be generated very rapidly by means of energy radiation absorption. The inventive method allows nanostructures and microstructures to be moulded on a substrate or be opened on a coated surface on structures in the nanometer range.

The invention relates to a method of shaping micro- and nanostructureson a layer, which is structurable by heat, by means of a structuredmoulding pattern, using electromagnetic radiation to generate therequired heat, such as is known for example from JP-A-2001 158044 orU.S. Pat. No. 5,078,947.

The exact shaping of micro- and nanostructures is achieved nowadays withmethods which have relatively high cycle times (hot stamping) or whichwork with initial materials which can make difficult the process controlof important parameters (e.g. polymerisation and temperature inUV-casting). In faster processes such as injection moulding, the shapingof smaller structures is in certain cases (e.g. structures with a highaspect ratio) not possible in an optimum manner or only possible withcost- and time-intensive dynamic preliminary heating of the tool.

In many applications of micro- and nanotechnology, methods are requiredwhich simultaneously permit rapid cycle times, precise shaping and alocal control of the heat supply to the location to be heated or to bestructured. This is for example the case if different substrates are tobe structured and connected together by the supply of heat withoutmutually impairing their individual functionality (microstructuredcomponents having functionalised surfaces, microchannels withbiologically or chemically active substrates as well as diffractivesurfaces, etc.). Rapidity and the quality of shaping are also theadvantages of nanolithographic embossing methods by comparison withserial methods such as direct electron-beam lithography. Innanolithographic embossing methods, precise control of the thickness ofthe residual layer and rapid multiplication of the structured pattern atvarious locations of a coated substrate are advantageous.

The object underlying the present invention, therefore, is to propose apossible way in which rapid and exact shaping of micro- andnanostructures is possible, especially with short process times andlocal control of the heat supply.

This object is accomplished according to the invention by a methodhaving the features of the main claim. Further advantageous embodimentscan be taken from the subordinate claims.

According to the method, a mechanically stable moulding pattern and astable layer carrier are used. The moulding pattern or the layer carrierare heated by absorption of a ray of high energy density only on thesurface because the ray has a small depth of penetration, such that thegenerated heat is transmitted to the layer. Then the softened layer isstructured by means of the moulding pattern, a layer being used which isas largely transmitting as possible for the ray and is penetrated by theray prior to the absorption in the moulding pattern. Thus in the method,only indirect heating of the structurable layer takes place. This occurseither due to the heating of the layer carrier or due to the penetrationof a heated moulding pattern. The energy density of the ray, which canbe achieved for example with a high capacity diode laser in the infraredrange, must be so high and the penetration depth of the surface must beso small that the substrate very quickly reaches the temperature andtemperature distribution which is necessary for the shaping of thedesired structures. Depending on the moulding pattern, this process issupported by a continuous or pulsating guidance of the beam. Here it ispossible through a suitable optical system to move a fine punctiform orlinear laser beam over the surface to be heated.

What is important here is that the heating is so short that substantialheat dissipation, which is a function of the heat conductivity of thesubstrate, and undesired heat distribution are avoided. Consequently theenergy supply and the heating which depends on same must be selected independence on the heat conductivity. For setting the process parameters,therefore, first the heat conductivity must be determined and then thecorrespondingly suitable process duration and supply energy must bedetermined in order to obtain the desired results.

The method permits very short cycle times and simultaneously a very goodshaping quality, the very low thermal inertia of the entire system andthe local and concentrated dynamic heating making this possible.

The layer which consists of a material which is sufficientlytransmitting for the radiation, for example polycarbonate or PMMA, canbe connected to an absorbent layer by this same radiation sourcedirectly after the shaping of the structures, such as e.g. during laserwelding, so that shaping and assembly can take place on the same device.

In the present case, it is not embossing alone which is understood undershaping. Due to the irradiation of semi-conductive materials, forexample silicon, which have a very small penetration depth for theradiation, at the irradiated surface, besides heat, charge carriers canalso be produced which induce electrohydrodynamic effects in a melt andin so doing can support the shaping.

By simple control/regulation of the radiation source, the heat supplycan be determined which is optimal for the material, the type ofstructures to be shaped and the type of connections. The continuous orpulsating guidance of the beam through a mask or suitable optical systemhere supports the delimitation of the heated surface.

In material technology, especially coating technology and in powdertechnology, transmitting and absorbent materials are still beingdeveloped which can be used for the method. It is also possible toprovide curved layer carriers and moulding patterns.

The invention is described in greater detail below with the aid ofembodiments, in conjunction with the accompanying drawings. Theserepresent:

FIG. 1 the shaping of micro- and nanostructures on a substrate;

FIG. 2 the nanolithographic shaping on ray-permeable layer carriers and

FIG. 3 the nanolithographic shaping on ray-absorbent layer carriers.

According to FIG. 1 a, a ray of heat 1 is guided through a ray-permeableplate 3, formed for example from quartz glass, and a ray-permeablesubstrate 4 pressed against this plate. Through a mask 2 or through asuitable optical system, the dimensions of the ray of energy can beadapted to the embossing pattern 5 located under same as the mouldingpattern. The embossing pattern 5, formed for example from silicon ornickel phosphorous, is very rapidly heated up by the absorption of theheat ray on the surface as a result of the low penetration depth. Micro-or nanostructures on the embossing pattern 5 can then be shaped onto thesubstrate 4 (FIG. 1 b). After the necessary cooling time, the shapedsubstrate 4 is removed from the embossing pattern 5 (FIG. 1 c). Inseries with the shaping process, features can be welded onto thesubstrate 4 by the direct absorption of the heat ray. The substrate 4represents in this method both the layer carrier and the structurablelayer.

In the embodiment according to FIG. 2 it is shown that the generation ofnanostructured resist masks is also possible by lithographic shapingaccording to the method. Here a ray-permeable plate 6 is coated with asuitable material, for example PMMA or polycarbonate. The energy ray 1penetrates the plate 6 and the layer 7 and heats the nanostructuredsurface, lying underneath same, of the embossing pattern 5 (FIG. 2a).Thereafter structures can be shaped into the layer 7 (FIGS. 1 b and 1c). By displacing the radiation source for the energy beam 1 and theembossing pattern 5 relative to the plate 6 and the layer 7, shapingscan be repeated at various locations and thus structures in thenanometre range can be replicated on larger surfaces.

FIG. 3 shows a possible way of producing a resist mask for aray-absorbent plate 8. For this purpose, this plate 8 is first coatedwith a suitable material 7 (FIG. 3a). The structured embossing pattern 9is in this case ray-permeable and can have a mask 2 on the upper side.Through this mask, deliberate guidance of the ray and thus a locallydefined heating-up of the ray-absorbent plate 8 can be achieved. Theresult of this is that the surface of the layer 7 can be melted locallyindependently of the dimension of the embossing pattern 9. This is veryadvantageous for shaping structures beside one another and thus beingable to multiply the structures in the nanometre range on largersurfaces. This comes about, similarly to Fig. 2, due to displacement inthe x-, y- and z-directions of the energy ray 1, the mask 2 and theembossing pattern 9 relative to the layer 7 and the plate 8 (FIGS. 3 band 3 c). The spacing between the individual shaped portions can be verysmall in this variant. As the energy source for the generation of thehigh-energy density, a high-capacity diode laser can be used for examplewhich emits in the infrared range.

In both variants of the nanolithographic shaping (FIGS. 2 and 3), thelow thermal inertia of the system permits an effective control of theresidual layer merely by purposeful guidance of the energy ray. Theshaped resist mask can be used as a pattern for nanostructuring thesubstrate by etching or electroforming.

1. Method of shaping micro- and nanostructures on a layer, which isstructurable by heat, by means of a structured moulding pattern (5, 9),using electromagnetic radiation to generate the required heat, wherein amechanically stable moulding pattern (5, 9) and a stable layer carrier(4, 6, 8) are used, the moulding pattern or the layer carrier is heatedby absorption of a ray (1) of high energy density, on the surfacebecause the ray has a small depth of penetration, the generated heat istransmitted to the layer (4, 7), and subsequently the softened layer isstructured by means of a moulding pattern, a layer being used which isas largely transmitting as possible for the ray and is penetrated by theray prior to the heating process.
 2. Method according to claim 1,characterized in that the moulding pattern (5, 9) or the layer carrier(4, 6, 8) is produced from silicon or nickel phosphorous.
 3. Methodaccording to claim 1, characterized in that the irradiated surface isdefined by a mask (2).
 4. Method according to claim 1, characterized inthat a structured moulding pattern (5, 9) is brought into the vicinityof the layer (4, 7), is in contact therewith or is pressed against thelayer, either the moulding pattern or the layer carriers beingpreviously heated.
 5. Method according to claim 1, characterized in thatthe radiation is transmitted additionally by the moulding pattern (9) orthe layer carrier (4, 6) and is accordingly absorbed by the layercarrier (8) or the moulding pattern (5) respectively.
 6. Methodaccording to claim 1, characterized in that a linear beam of energy ismoved at least once over the moulding pattern.
 7. Method according toclaim 1, characterized in that the irradiated surface is irradiated overthe area by a suitable optical system.